The present invention relates in general to wireless cellular systems and in particular to methods and systems for assigning the most appropriate traffic channel frequency, in systems using multiple beams to cover a given cell or sector of a cell, to a MS (mobile station) that may be located within the field of coverage of any of said multiple beams.
As cellular system technology becomes more popular, more and more customers need to use the systems simultaneously. One solution was to make cell sizes smaller to thus increase the number of cells thereby increasing the number of customers that may use MSs (mobile stations) simultaneously. Another solution was to use TDM (time division multiplex) to permit communication with more than one customer per channel of allotted frequency. A further potential solution has been to divide a cell into different sectors and where each sector in essence may operate in a manner similar to creating a smaller cell for the area covered by a sector. It is presently quite common for each cell to be divided into three sectors in urban areas. In such situations, a separate control channel frequency is used for each sector.
Since a system is only allowed a given number of frequency channels, each control channel required for system operation lessens the number of channels available for general traffic.
It has been proposed that a sector may be further subdivided using narrow beam antennas with a separate control channel for each sub-sector. The narrow beams help limit the amount of RF interference in the system and thus increase total system capacity for a given number of traffic channels available. While there should not be any technical reason why such a system would not operate, the large number of control channels required makes such a configuration impractical.
The control channels are used for communications between the mobile unit and the antenna/base station or BTS (base transceiver station). As set forth in an industry standard designated as IS-136, this function is provided by the digital control channel (DCCH). The DCCH is a continuous data stream that provides the system identity and configuration information needed by all users. It also provides paging information that alerts mobile units about the presence of incoming calls. The control channels are defined in terms of reverse and forward control channels. The forward control channel (FCCH), also known as forward DCCH, provides information from the cell site base station to the user. This is known as xe2x80x9cdownlinkxe2x80x9d information.
The reverse control channel (RCCH), also known as reverse DCCH, provides information from the mobile unit to the cell site, known as xe2x80x9cuplinkxe2x80x9d information. The RCCH is mainly used for access requests such as call initiations, page responses, and registration of information as the mobile unit crosses cell boundaries.
One of the functions provided by the DCCH is to relay information related to Mobile Assisted Channel Allocations (MACA). At the present time, the forward MACA message, known as the MACA List, provides each mobile unit with a list of traffic channels which it can use in a particular cell when it is within the boundaries of that cell. When a mobile unit enters a cell""s boundaries, it receives an overhead message from the base station with a request to forward its MACA report with any of 4 specified mobile generated messages (origination, page response, registration, and audit response). The MACA report provides the signal strength measurement for the traffic channels in the received MACA list. This information is presently utilized in determining which channel will become the traffic communications channel for the mobile unit.
When a mobile unit, in a TDMA (time division multiplex access) cellular system, begins transmitting on a traffic channel, the base station sends a list of adjacent DCCHs, known as the MAHO List, followed by a start measurement order on the forward FACCH (fast associated control channel). Once every second, the mobile unit responds with CQMs (Channel Quality Messages) on the reverse SACCH (slow associated control channel) which provide the signal strength measurement for each DCCH in the requested MAHO List. The base station presently uses this CQM data to determine when the mobile unit should be transferred (handed-off) to another cell.
Older wireless systems, operating under a prior standard designated as IS-54 use an analog control channel referred to as ACCH. Such systems do not include MACA capabilities.
Systems presently operating under either the IS-54 or IS-136 use at least one control channel per antenna beam generated for assigning traffic channels to MSs operating within the cellular coverage area of a BTS.
These and other disadvantages are overcome by the present invention. In one aspect of the invention, method and apparatus are provided for assigning MSs roaming throughout the area covered by multiple beams, the appropriate traffic frequency while reducing the number of control channels required to cover the multiple beam area to less than one control channel per antenna beam.